Lecture 5 and 6 Flashcards
By weight, what do chromosomes contain more of?
Protein (more than DNA)
Why did people think proteins were the genetic material?
20 subunits (greater no. combinations), chromosomes contain more protein then DNA
Who studied pathogenic strains of bacterium?
Frederick Griffith (1928)
What bacteria did Frederick Griffith conduct experiments on?
Smooth virulent and rough nonvirulent strains of Streptoccus pneumoniae
What did Frederick Griffith find?
Dead virulent bacteria mixed with nonvirulent bacteria killed the mice
What did Frederick Griffith’s experiment demonstrate?
‘transforming principle’ was a chemical
Who investigated which component of the bacteria was responsible for the transforming activity seen in Griffith’s experiments?
Oswald Avery and McCarty
What did Oswald Avery and McCarty do?
Fractionated cell-free extracts of S-strain bacteria, only nucleic acid was capable of causing transformation
How did Avery and McCarty further prove nucleic acid was causing the transformation?
Eliminated the transforming activity with deoxyribonuclease (degrades DNA)
How did Avery and McCarty prove proteins weren’t causing transformation?
They used protease to break down the proteins, transformation still occured
Who provided evidence that DNA is the genetic material?
Hershey and Chase (1952)
What organisms did Hershey and Chase use in their experiments?
Bacteriophage T2 and E.coli
What does T2 proteins contain?
Sulfur in its amino acids (methionine and cysteine)
What does T2 DNA contain that its protiens do not?
Phosphorus
How did Hershey and Chase label the T2’s proteins?
Radioactive isotope sulfur-35
How did Hershey and chase label the phages DNA?
Isotope phophorus 32
What happened in Hershey and chase’s experiment?
Radioactivity recovered in host and passed onto phage progeny when grown labelled with phosphorus-32
What does DNA always consist of?
The same six basic chemical components: phosphate group, five carbon pentose, nitrogenous base
What did Rosalind Franklin (and Maurice) produce?
X-ray diffraction patterns from DNA fibers
Who concluded that A always binds to T and C to G?
Chargaff, using Chargaff’s ratios
When did Watson and Crick propose their double helix model of DNA structure?
1953
How often do DNA strands wrap around each other?
30 angstroms, every 10 base pairs
What are the three stop codons?
UAG, UAA and UGA (terminate translation)
What code specifies the reading frame?
Initiation codon UAG
What amino acid is encoded for by UAG?
Methionine
